In recent years, the social consciousness of the environment and energy-saving has been enhanced, and efforts have been activated for realizing optimum energy supply by monitoring the emissions of greenhouse gas, such as CO2, or collecting information, such as power consumption, from time to time. In view of this, in order to accurately and immediately collecting information, such as green house gas emissions or power consumption, a technique referred to as a sensor network has been studied and developed.
A system of the sensor network includes a plurality of sensors provided in a target area, a plurality of relay node devices including a connection interface to the provided sensors, a gateway connecting the plurality of relay node devices and a server, and a server collecting data detected by the sensors.
In the sensor network system, an ad-hoc communication technology can be used. In the sensor network system using the ad-hoc communication technology, the relay node device recognizes a relay node device adjacent to the own node device and autonomously constructs a network, and monitors communication quality or a communication failure with the adjacent relay node device and autonomously selects a communication path.
A place to be detected by the sensor is, for example, a dangerous area, such as a river or a cliff, an area in soil, an area under water, or an area in a structure. When the sensor is provided in the area described above, it is difficult in some cases that a relay node connected to the sensor performs data transfer to or from an adjacent relay node device using a wireless communication system. In addition, when a relay node device is configured to be driven by a power source incorporated into the own device, the relay node device stops operating due to the life of the power source.
In order to solve the inconveniences described above, a power supply device that supplies power to each of the relay node devices is provided in the sensor network system, and a wired ad-hoc network in which adjacent relay node devices are connected by wired cables is used. On each of the wired cables connecting the adjacent relay node devices, a signal line and a feeder line may be mounted using, for example, the Power Over Ethernet (POE) technology.
When multiple sensors are provided in the wired sensor network system, the number of relay node devices connected to the sensors is also increased, and therefore it is complicated to manually start the multiple relay node devices. In addition, in the wired sensor network system, when the sensors are provided in a dangerous area, such as a river or a cliff, in soil, under water, or in a structure, it is difficult to manually start each of the plural relay node devices connected to the sensors. In view of the foregoing, the plural relay node devices are configured to be started by supplying power from a power supply device to the respective relay node devices through wired cables connecting relay node devices adjacent to each other.
However, when power needed for starting each of the relay node devices is supplied simultaneously from the power supply device, a large current from the power supply device flows at once into a root relay node device connected near the power supply device. For that reason, in the relay node devices near the root, the temporary large current from the power supply device becomes a rush current, and the relay node devices near the root are likely to not be started normally. In addition, relay node devices near a terminal that receive power supply via other relay node devices are likely to not be started normally due to voltage drop or the like.
In view of the foregoing, the power supply from the power supply device to each of the relay node devices in the wired ad-hoc network system needs to be controlled such that each of the relay node devices is normally started.